Synchronizing apparatus



Feb. 4, 1941. M. ARTZT smcnnomzme APPARATUS 4- Sheets-She'et 3 Filed June 21, 1939 INVEN TOR. mu? .4R77T ATTORNEY.

Feb. 4, 1941. M. ARTZT smcnaomzme APPARATUS Filed June 21, 1939 4 Sheets-Sheet 4 Z 1 SIGNAL 20 f 20 INVEN TOR. MAURICE ARTZT ATTORNEY.

Patented ab. 4, 1941 PATENT orrlc z SYNCHRONIZIN G APPARATUS Maurice Artzt, Haddonfleld, N. 1., assignor m Radio Corporation of America, a corporation of Delaware Application June 21, 1939, Serial No. 280,304

12 Claims.

My invention relates in general to apparatus for synchronizing the movement of two prime movers, and more particularly to such apparatus as applied to the operation of two or more electric motors.

In a number of fields of activity, it is necessary to operate prime movers in synchronism. This is particularly true where such prime movers comprise electric motors. In a number of dem vices, the electric motors must be operated at the same speed, and.in others the devices must be operated not only at the same speed but cophasally. Accordingly, it is one of the objects of my invention to provide an apparatus which 15 will accurately synchronize both as to speed and phase the movement of two prime movers.

One of the fields in which mechanical apparatus must move not only synchronously with respect to speed but also in a co-phasal relation- 20 ship in the facsimile field, or the field in which images are transmitted and recorded. In general, such apparatus comprise a transmitter which linearly scans the image to be transmitted and a receiver which is adapted to be actuated 25 by the signals developed from the transmitter to reproduce elemental optical areas in a linear fashion which follows the movement of the transmitter scanning arrangement. It will be apprecia ed that in order that a true and undistorted optical image is reproduced, the movement of the recorder must not only be the same in speed as that of the scanning apparatus but must be operatedco-phasally with respect thereto. Accordingly, it is another of the objects of my invention to provide a synchronizing apparatus and arrangement which will be particularly adaptable for use in the facsimile field.

One of the methods suggested for synchronizing facsimile apparatus is to utilize the same 40 power line which is supplying the motor at the transmitter to supply also the driving motor of the receiver and thus maintain a phase relationship between the two driving motors. One of the disadvantages of such a system is the fact that it definitely limits the area in which receivers can be operated, and in large cities where this' might ordinarily be feasible, it is not uncommon to have two or more power supplies which are 50 entirely independent and do not maintain a definite phase relationship each with the other. Accordingly, it is another of the objects of my invention to provide a device which will not be dependent upon the use of a common power sup- 5 ply to synchronize two driving motors which must be operated in synchronism both as to speed and phase.

Some commercial facsimile systems at the present time are maintained in synchronism by the use of tuning forks which are accurately adjusted and which are maintained in a related set of conditions with respect to temperature, humidity and the like. This often involves the use of complex and highly critical temperature control apparatus and, hence, is not adapted for use on a large scale such as in the ordinary home where facsimile receivers are now finding ready use Accordingly, it is another of the objects of my invention to provide a synchronizing apparatus which will be relatively simple, accurate, and will avoid the use of complex apparatus.

Also, it is for some purposes such, for instance, as the transmission of secret telephony and telegraphy desirable to accurately control the .rate of oscillation of an oscillating circuit. Again,

it is desirable from a standpoint of remote control to be able to definitely afiect the period of oscillation of such an oscillator. Accordingly, it is another of the objects of my invention to provide a device for the easy control of oscillators by signals transmitted from an external source. In summary, the objects of my invention are as follows:

1. To provide an apparatus which will accurately synchronize, both as to speed and phase,

the movement of two prime movers.

2. To provide a synchronizing apparatus and I arrangement which will be particularly adaptable for use in the facsimile field.

3. To provide a device which will not be dependent upon the use of a common power supply to synchronize two driving motors which must be operated in synchronism both as to speed and phase.

4. To provide a synchronizing apparatus which will be relatively simple, accurate, and will avoid the use of .complex apparatus.

5. To provide a device for the easy control of oscillators by signals transmitted from an ex-- ternal source.

The operation of my device in general is as follows: For purposes of clarity, the motor such as is used at a facsimile transmitter may be called the first motor, and the motor at the receiver and which must be synchronized therewith as to speed and phase may be termed the second motor. Expressed differently, the second motor comprises a prime mover whose speed and phase must be substantially identical with a first motor with whose operation it is desired to be synchronized.

A signal is developed and transmitted, which represents a definite position of the first motor. and this signal is sent at recurrent intervals. A signal is developed at the second motor which is representative of the position of the second motor at a particular time; and these two signals are compared as to time in such a fashion that an electrical quantity is stored whose amplitude and polarity indicate both the direction and amount of deviation in the operation as to speed and phase of the second motor with respect to the first. This stored signal is used to operate corrective apparatus, the latter being adapted to change the speed, and hence the phase of the second motor with respect to the first motor when non-synchronous operation occurs.

My invention will best be understood by reference to the figures in which Fig. 1 is a schematic representation of a comparing circuit,

Fig. 2 is another embodiment of such a comparing circuit,

Fig. 3 is an embodiment of my invention, and

Fig. 4 is a second embodiment of my invention,

Fig. 5 is a further embodiment of my invention.

Referring to Fig. 1, there is shown one embodiment of a circuit for camparing the received signal which has been generated in accordance with the position of a first prime mover with the position of a second prime mover. This typeof arrangement has been especially adapted for use for so-called facsimile apparatus. The motor which drives the scanner, drives the elements thereof so that once for every scanned line, there is developed a signal, which identifies the position of the motor armature. It has been found convenient to generate this signal by merely taking the steady amplitude signal which results when clamping members which hold the picture to be transmitted on the drum pass by the scanning means. Since the position of these clamps is fixed, it will be appreciated that this clearly defines the position of the driving motor armature during at least a portion of its cycle of operation.

In general, the comparison is made between the received signal and a signal developed at the receiver, the latter being dependent-upon the position of the driving motor armature at the receiver. A bridge arrangement is used in general. However, the showing of Fig. 1 does not include such a bridge. If the motors are operated synchronously, that is to say, with the proper speed and phase, the bridge remains balanced. If the motors are not operating synchronously, the comparison is caused to develop an energy whose value is dependent upon the degree of divergence between the operation of the two motors.

In Fig. 1, the receiver signal is impressed on the primary of a transformer I0, the secondary thereof having its terminals connected to the plates II and I2 of a duo-diode-triode tube l3. The center tap from the secondary is connected to the control grid ll of the tube Band is connected to two time constant circuits, the first comprising condenser l5 and resistor i6, and the second comprising condenser H and resistor l8. These two time constant circuits are connected serially and the cathode [9 of -a duo-diode-triode is connected to the terminal where the two time constant circuits are joined to each other. The anode 20 of the-triode section of the tube I3 is connected to a brush member 2| which is positioned adjacent a second brush member 22,

the two brushes being adapted to co-act with a commutator which is shown in this figure and has a conducting section 23 and an insulating section 24. Brush 22 is connected to the positive side of the plate supply potential and, as indicated here by the symbol +13, the negative side of the plate supply being grounded. The commutator is rotated through appropriate driving means by the driving motor which is desired to be synchronized with the motor which causes the development of the recurring signal. I The conducting section 23 closes the plate circuit of the triode section of the tube l3 once per scanning line of the device for a length of time slightly less than the length of the framing line signal. If the two motors are in phase, thecommutator of the conducting section will be at the center when the transmitted signal arrives and biases the tube to cut-01f. This will leave a definite charge on condenser H, and the value of the voltage across the time constant circuit l1, l8 will be at its natural positon of half value.

If the motor tends to speed up, the conducting section of the commutator closes the contacts 2! and 22 earlier during the next revolution and the condenser i1 is charged for a longer period of time before the arrival of the signal biases the tube l3 to cut-off. Thus, ec will rise in average value. Likewise, a slowing down of the motor will lower the average charge time of condenser l1 and lower 6c. The changing voltage cc is then passed on to control the motor speed through one of the systems which will be described more fully hereinafter. The chief advantage of this circuit is simplicity. In this particular circuit, the resistor l8 must be set to bleed the condenser II to a voltage lower than the next control pulse so that correction can be made for slowing down or speeding up.

A refinement of this circuit can be made by fixing the zero value of the control voltage at some predetermined point and not depend on an averaging effect of the system.

Referring to Fig. 2, there is shown a true bridge arrangement for comparing the received signal with the position of the driving motor at the receiver. In this figure, the received signal is impressed on the primary of a transformer 30, the secondary of which is connected at its terminals to the plate members 31 and 32 comprising the diode sections of a duo-diode-triode 33. The center tap from the secondary is connected to the control grid 34 of the triode section of the tube 33 and also at the same terminal is connected to a resistance-condenser combination comprising condenser 35 and resistance 36. The other terminal of the resistance-condenser combination is connected to the cathode of the tube which in turn is grounded at the point 31. The anode 38 of the triode section of the tube 33 is connected to a brush member 39 which is one of three brushes, the other two brushes being brushes 40 and 4|, all three of the brushes being adapted to coact with a commutator having an L-shaped conducting section 42 and an insulating section 4E3. This commutator is driven by the receiver driving motor. The brush 40 is connected to a resistance-condenser parallel combination comprising condenser and resistance 45. The other terminal of this combination is connected to the common terminal of two sources of potential 46 and 41 which, in this case, may be batteries. The negative terminal of the battery 46 is grounded at 31.

The positive terminal of battery 41 75.

, that any brush wear will not cause the arrangement to close the circuits in an incorrect timing v relationship.

The action of the device is as follows: In effect, brushes 39, 40, and 4| contact the conducting section 42 of the commutator at the same time closing the circuit comprising anode 38, brushes 39, 48 and 4|, the resistance-condenser combination 44 and 45, and, the potential supplies 46 and 41, and accordingly the conducting segment 42 will be at the same potential as the connection between batteries 46 and 41, and the condenser 44 receives no charge. At a later time the signal arrives and biases the tube to cut-off, opening the lower side of the bridge system. If the recorder is in exact frame, in other words, if the driving motor at the receiver is in proper phase relationship with the driving motor at the transmitter, the insulating section of the commutator will open the brush 4| and the upper side of the bridge at this same time, and the condenser 44 will not receive an additional charge, in view of the fact that both sides of the bridge are opened together. If the recorder were fast, the brush 4| would be opened before the received signal biases the triode section of the tube 33 to cut-off and the condenser 44 would receive a negative charge through the tube and brushes 39 and 40. If the recorder were slow, the triode section of the tube 33 would be cut-off first, and the condenser 44 would receive a positive charge through the brushes 40 and 4|. If the resistance 48 is equal to the plate resistance of the triode section of the tube 33, the same error whether fast or slow will leave the condenser 44 with the same charge voltage but of a polarity determined by. whether the time error was fast or slow. The circuit constants are so arranged that the condenser 44 is charged essentially at a constant .current and, therefore, the control voltage E will be directly proportional to the time error. The resistor 45 is high in value compared to the resistor 48 and the tube resistance, and gradually discharges the condenser 44 to a zero value during the picture portion of the scanning line. In this Way, when this apparatus is applied to the facsimile field, the correction applied at the start of each scanning line is directly proportional to the time error of a scanning line just received.

Referring to Fig. 3, there is shown one embodiment of my invention. In this embodiment, the rectified signal from the printer amplifier is impressed onto a resistor 60, this resistor being connected to the cathode 6| of a threshold rectifier 62, the plate of the rectifier being connected to one terminal of a resistor 63 and to the control grid 64 of tube 65. The other terminal of the resistor is grounded at 66. The anode 61 of the tube 65 is connected to a brush member 68 which comprises. one of the three brushes 68, 69 and I0,

the latter being 50 positioned as to remain in contact with the commutating member having a conducting portion II and an insulating portion I2. The brush'69 is connected to one terminal of a variable resistor I3 by means of which the sensitivity is controlled, and the other terminal of the resistor I3 is connected to one terminal of a resistance-condenser combination comprising resistance I4 and condenser I5, this combination acting to store the corrective impulse when the device is out. of. synchronous operation. The other terminal of the resistance-condenser combination I4 and I5 is connected to one terminal of a resistance I6, and the latter is connected serially with a potentiometer II, the terminal remote from that connected to resistor I6 being grounded through a condenser I8. The sliding contact of the resistor 11 is connected to ground. The third brush member ID is connected serially with a resistor I9, the other terminal of the resistor I9 being connected to one terminal of a resistor and to one electrode of a glow tube 8|, and to a further resistor 82, the resistors I9, 80, 82 and the glow tube 8| having one terminal in common. The other electrode of the glow tube 8| is connected to an electrode of the glow tube 83, and the common connection is'connected to one terminal of the resistor I6 and one terminal of the resistance-condenser combination 14-15. as illustrated. The other electrode of the glow tube 83 not connected with the glow tube 8| is in turn connected to one terminal of the resistor 11. In addition, this latter electrode is also connected to one terminal of a filter inductance 84 and filter condensers 85 and 86, the terminal of the inductive member 84 remote from this connection with the glow tube 83 being connected to the negative side of the source of energy.

The terminal of the resistance 82, which is remote from the terminal connected to the glow tube 8|, is connected in turn to filter condenser 85 and 86 and to the positive side of the supply voltage. shunted across the resistance-condenser combination I4 and I5 are a pair of leads 8? and 88, one of these leads being connected to the common cathode terminal of the oscillator tube 89 and the load tube 90. The lead 81 is connected to the control grid of the load tube 96. The anode of the tube 98 is connected through a resistance 9| to the anode 92 of the oscillator tube 89. The oscillating tube 89 has its plate connected back to its cathode serially through two condensers 93 and 94. Connected in parallel with the condenser 93 is a tapped section of an inductive member 95, variations in the inductive member being fed to the grids of two tubes connected in push-pull through condensers 96.

from that connected to the resistance 99, is

joined to one terminal of an inductive member IIlI which is interposed in inductive relationship with the inductive member 95, the other terminal of the inductive member IIlI being connected to the terminal of the resistance 99 remote from the cathode connection. A pair of push-pull amplifying tubes I83 and N14 have the control grids thereofconnected to one side of the condensers 96 and 91 respectively, and to one terminal of serially connected resistors I05 and I86, the common terminal of the latter being connected to the cathodes of the tubes I 93 and I04 through a condenser I01. The'terminal of the condenser I01 remote from that connected to the cathodes of the tubes I03 and I04 is connected to the negative side of the voltage supply through a resistance I08. The anodes of the tubes I03 and III! are connected in push-pull to the terminal of transformer I09, the center tap of this terminal being connected through the actuating coil III! of a relay to the positive side of the voltage supply.

The secondary of the transformer is connected so as to drive a motor III, and one side of a. power supply system is connected to one terminal of the motor III, and the other is connected to one contact II2 which is adapted to be closed or opened by the armature I I3 of the relay whose activating coil is IIII. This armature also closes the contact Ill which is connected to one terminal of the secondary of transformer I09.

In the arrangement illustrated in Fig.3, the

signal used as a source of control is the voltage supplied to the grid of the white printer tube in the printer amplifier, and reference should be had here to my copending application Serial No. 133,135 filed March 26, 1937. This varies from zero on white to about twenty volts negative on black. The framing line is fully black and, therefore, twenty volts is delivered to the resistor 60 during the framing line. The threshold rectifier 62 is introduced to prevent noise of any value less than about 60% of this twenty volts from affecting the control tube 64. The threshold setting is determined by the setting of the moving contact on resistor TI. The tube 65 and commutator circuit of the brushes 68 and 69 form one-half of the bridge, theother half being furnished by the circuit of the brushes 69 and I0, and the resistor I9. The resistor I9 is set in value to equal the plate resistance of the tube 65 with no signal, and thus to balance the bridge. The two halves of the bridge are held balanced by the glow tube regulators III and 83. The output voltage of the bridgeis obtained from the resistancecapacity combination I4 and I5, and the resistance I3 is used to set the over-all amplification of the system. The oscillator 89 uses a conventionally tuned plate circuit and is self-biased by the resistance-condenser combination 99 and I00. The potentiometer 98 adjusts the grid drive and controls .the frequency over a fairly wide range. By varying the value of resistor and resistor 99, and by readjusting the frequency of the oscillator to a desired number of cycles which in practice has been 60, the change of rate of drift of frequency of the oscillator with line voltage can be brought to a minimum. This adjustment must be made with the load tube 9!! drawing its normal load from the oscillator through a resistor H5 which has one terminal thereof connected to the cathode of tube and the other terminal thereof connected to one terminal of the resistor 99. This is not critical.

As well as regulating the bridge voltages, the two glow tubes BI and 83 regulate the oscillator plate supply and the load tube.

The output stage, which in practice has comprised two 6L ii-G tubes connected in Dushpull is excited directly from the oscillator and is biased by the voltage drop in the filter reactor 84. The-output transformer has been especially designed to deliver a full volts to the standard motor used when the motor is properly tuned by its capacitor II I. In practice, the total load on the 400 volt supply is 215 milliamperes of which the output stage draws milliamperes plate current and twenty milliamperes screen current. Total plate and screen load of this stage has been 72 watts, and the output realized is 25 watts in the motor, 3 watts in the output transformer and 2 watts in the screen resistor II8. Thus, the plate dissipation of the tube is 21 watts, which is within the tube rating. The motor when stalled oflers too low an impedance to the transformer I09 which so reduces the voltage that the system is not self-starting. To overcome this, a relay is provided which starts the motor on the nonsynchronous 110 volt 60 cycle supply illustrated, and when the tubes I03 and I04 have warmed up, the coil IIIl actuates the armature II3 which normally is in contact with the contactor I I2 and thus switches the supply to the motor to the transformer.

It will be appreciated that the bridge circuit which develops the corrective voltage operates similarly to the bridge as illustrated in Fig. 2 to develop a corrective signal by storing energy in the condenser I5, whose polarity is determined by whether the motor is operating too fast or too slow. If the motor runs slow, the direction of the signal is such that the control grid of tube 90 is rendered more positive and thus draws more current from the oscillator tube, and in efiect lessens the inductance of the tank circuit of the oscillator and hence the frequency of oscillation is raised, which tends to speed the motor up. The reverse is true if the motor is running fast, the charge on condenser I5 is stored in such a direction as to bias the grid of tube 90 more negatively, hence the load tube draws less current from the oscillator, and the effect is that the inductance of the tank circuit is increased, and hence its frequency of oscillation is' decreased, and the motor is slowed down.

If the machine is completely out of frame so that no signals come in during the time when a conducting portion of the commutator is in contact with one of the brush members, the oscillator or other control device is set for the extreme slow position by a maximum charge being impressed on the storage capacitor in the slow direction. This will cause the recorder motor to run slowly enough to come to a position gradually where the commutator overlaps the received signal, and from this position it will come into exact frame by the slow or fast action of the corrections then applied. Thus the recorder seeks the frame position, and then synchronizes on this exactly.

Referring to Fig. 4, there is shown another embodiment of my invention. The corrective signal developing circuit in this figure is somewhat similar to that disclosed in Fig. 2. The batteries 46 and 41 of Fig. 2 have been supplanted by glow tubes, and a triode arrangement is used rather than a duo-diode-triode, and the signal is impressed onto a time constant circuit in the control grid-cathode circuit of the triode.

, In the figure, the input signal is impressed on a. resistor I20 which has one terminal thereof connected to the control grid of a triode I2I, and the other terminal thereof connected to ground. Connected in parallel with the resistor is a condenser I22. The anode of tube IZI is connected serially to a brush member I23, the brush member being one of three brushes I23, I24 and I25, which are adapted to co-act with a commutator having at least one L-shaped conductor I26 and an insulating section I27. The brush member I24 is connected serially to a resistor-condenser combination I28 and I29 respectively, the condenser being adapted to store the corrective charge. The terminal of the resistance-condenser combination I28 and I29, which is remote to that connected to the brush I24, is connected to ground at I30 through a condenser I3I. The brush member I25 is connected serially with the variable resistor I32, the latter having the terminal thereof remote from that connected to the brush member I25 connected to one electrode of a glow discharge tube I33. The other electrode of the glow discharge tube is connected to the terminal of the resistance-condenser combination I28 and I29 which is remote from the terminal connected to the brush member I24. Also connected to this terminal is one electrode of a second glow tube I34 and the other electrode thereof is grounded. The electrode of glow tube I33, which is connected to one terminal of variable resistor I32 is connected through a resistance I35 to the cathode of a full wave rectifying tube I36.

The tube I36 has the normal apparatus associated therewith for rectifying an alternating current supply wave, the cathode thereof being heated from one secondary of a transformer I31, the other secondary thereof having its terminals connected to two anode members I38 and I39. Shunted across the, rectified output are three condensers I40, I and I42 which are filter condensers, and a filter choke I43 is connected serially with one side of theline which is grounded at I44. Also serially connected with the filter choke is a biasing resistor I45'having the terminal thereof remote from the terminal connected to the filter choke I43 connectedto a bias resistor I46, the latter being grounded through the filter condenser I41. The elements I35 through I46 comprise the power supply for the apparatus.

The terminal of resistor I32, which is remote from the terminal thereof connected to brush I25, is connected to the anode of a thermionic tube I58 having a resistance I5I connected serially with the two anodic sections I52 and I53. The control grid of this tube is connected through a resistor I54 to one terminal of the resistancecondenser combination I28 and I29. The cathode of the tube has a resistor I55 serially connected therewith. This tube comprises theso-called magic eye type of tube, and its function will be explained more in detail hereinafter. The control grid of the tube I50 is also connected 1130 the control grid of the load tube I56, and hence is connected through resistor I54 to one terminal of the resistance-condenser combination I28 and I29. The load tube has the anode thereof connected to the anode of oscillator tube I51 through a resistance member I58. The cathode of the load tube I56 is connected through resistor I59 to one terminal of the resistor I55. The control grid of the oscillator tube I51 is connected to the sliding arm of a potentiometer I60, the potentiometer having one of its terminals connected through resistor I6I and resistor I62 to the cathode of tube I51. The common terminal of resistors I6I and I62 is connected to the common terminal of resistors I55 and I59. The resistance I62 has a condenser I63 shunted in parallel therewith, and this resistance-condenser combination acts as a self-biasing arrangement. The terminal of potentiometer I60, remote from the terminal thereof connected to the resistance I6I, is connected to one terminal of an inductive member I64 having a tap associated therewith, the tap member being connected back to cathode of the tube I51 through the resistance I62. The anode of tube I 51 is connected to one terminal of an inductance I65 which is inductively associated with the inductance I64. This inductance has a tapped section,

case, is illustrated as a screen grid tube.

and the tapping terminal is connected to one terminal of a condenser I66 which has its other terminal connected to the anode, and also the tapping section is connected to one terminal of a condenser I61, the other terminal thereof being connected to the common terminal of resistors I6I and I62. The common terminal of resistance I6I and I62 is connected to the terminal of the resistance-condenser combination I28 and I29 remote from the terminal thereof which is connected to the grid of the load tube I56. The anodes of tubes I56 and I51 are energized by electrically connecting the anodes to the positive side of the power supply through resistor I68. The output of the oscillator is fed to the control grid of an amplifying tube I1I which, in this The plate circuit inductance I65 of tube I51 has one terminal thereof connected to the control grid of tube "I through condenser I12 and resistor I13. The common terminal of condenser I12 and I13 is connected through resistor I14 to the common terminal of resistor I46 and condenser I41.

The cathode of tube IN is grounded. The screen grid of tube I1I is energized from the positive side of the supply through a resistor I15. The anode of tube I1I is grounded through a condenser I16 and is also connected to the positive side of the supply line through a coil member I11. The coil member controls the vibration of an armature I18 which is associated with two contacts I19 and I80. The contact I19 is connected to the armature through a resistor I8I and a condenser I82. The armature and one terminal of the condenser is grounded at I83. The contacter I is connected or is grounded at the point I83 through a resistor I84 and a condenser I85, the condenser I85 and the condenser I82 having a common terminal. shunted in parallel with the series combination of condensers I82 and I 85 is the primary I86 of a transformer, and the center tap of the primary is connected to the cathode of tube I36 through an inductive member I81, the inductance being grounded at each terminal thereof through condensers I88 and I89 respectively. The output from the transformer whose secondary is I90 is used to drive the motor synchronously. Ihe resistors I8I, I84 and condensers I82, I85 are used as spark suppressors for the vibrator; and the inductance I81, and the condensers I88 and I89 form a filter.

The operation of the device is' as follows: With synchronous operation, the top. of the L-shaped conducting segment I26 should just open the circuit of the brush I 25 simultaneously with the beginning of the synchronizing signal, and the signal should last for a time until the brushes I23 and I24 are opened by the insulating section of the commutator, that is to say, they have just passed the edge of the L-shaped conductor. If the machine is in synchronsim, the effect of the opening of the circuit of the brush I 25 which normally would unbalance the bridge is offset by the effect of the synchronizing signal in driving the tube I 2I to cut-off. Consequently, the bridge remains balanced and no charge is stored in the condenser I29.

On the other hand, if the machine is operating too fast, the circuit of the brush I 25 is opened while brushes I23 and I24 remain closed. This means that the anode circuit of tube I 2I is closed while the tube is conducting, and as a consequence the bridge comprising the internal resistance of tube I2I, resistance I32, glow lamps motor.

I33 and I34 is unbalanced, and there is impressed across condenser I26 a voltage which charges the condenser to a degree depending upon the length of time that tube I2I is conducting. If the machine is only slightly fast, a

synchronizing signal will come in while tube I2I is conducting for only a short period of time, and as a coiisequence the charge accumulated on the condenser I29 will be small. This charge is in such a direction as to bias the grid of tube I56 negatively, and the tube I56 being a load tube draws less current from the plate of tube I51 which effectively changes the inductance of the tank circuit of the oscillator tube I51 so as to decrease the natural period of oscillation of the oscillator, thus slowing down the vibrator armature I18 and thus slowing down the driving On the other hand, if the device is operating slowly, the synchronizing signal will come in and drive the tube I2I to cut-off while brushes I24 and I25 are still in contact with the conducting section I26 of the commutator, and the result will be that the bridge is unbalanced and that a charge will be stored in the direction opposite to that which is stored when the brush I25 is open and the tube I2I is conducting. This charge is in such a direction as to bias the grid of the tube I56 positively, and hence this tube draws more current from the oscillator tube I51 and effectively changes the inductance of the tank circuit so that the oscillator period of oscillation is increased. Consequently, the armature I18 is vibrated more rapidly, and thus passes to the driving motor a higher frequency than when the device is operating synchronously.

Tube.I50 is the so-called magic eye type of ,,tube which gives a light and, shadow portion which is proportional to the potential impressed on the grid of the tube. The parameters of resistance I55 are chosen so that the eye is open half way of its total swing. It will be observed from the drawing that the corrective pulses go not only to the grid of tube I56 but also to the grid of this tube I50. The eye will then close or open to an extent depending upon the direction of the charge on the terminal of the condenser I29 to which the grid of tube I50 is connected. Hence, a visual indication is given of the direction of the correction needed, that is to say, as to whether the device is operating slowly or too speedily.

It will be appreciated that there are a number of modifications that well fall within the spirit and scope of the invention. For instance, the commutator might be entirely conducting with the exception of a small insulating section having the width of the upper section of the L-shaped conductor illustrated in Fig. 4, and a lower insulating section which would contact with brush I23 and which would be of the width of the presently shown conducting sections. The tube I2I might be biased to cut oil and could be rendered conducting by the synchronizing signal instead of the presently illustrated system wherein the tube is driven to cut-off.

Again, the corrective voltage need not change the frequency of an oscillator as is done here, but might very well be used to vary the voltage supplied to a motor. It will be appreciated that all such arrangements will fall fairly within the spirit and scope of my invention.

Due to the high capacity of condenser I29, the correction being applied once per cycle of the movement of the commutator is illustrated here,

such position as to be co-operatively associated with the commutator member having an L- shaped conducting segment 205 and an insulating segment 206. The commutating member is driven through appropriate gearing means 201 by the recorder motor 208 which has on the shaft thereof a fiyball governor 209 to which is fastened a disc member 2I0.

The brush member 203 is connected to the control grid of a thermionic tube MI and is also connected to the cathode thereof through a. re-

sistance-condenser combination comprising a resistance 2I2 and a condenser 2I3. The terminal of the resistance-condenser combination remote from the terminal which joins the brush member 203 being connected to the cathode of tube 2 through a resistor 2I5. The brush member 204 is connected through a resistor 2I6 to the positive terminal of a source of potential 2I1 whose negative terminal is connected to the terminal of the resistance-condenser combination 2 I 2 and 2 I3 remote from the terminal thereof connected to the brush member 203. The common terminal of the potential supply 2" and the resistance-condenser combination is also connected to the positive terminal of a second source of potential supply '2I8 whose negative terminal is grounded. The common terminal of the resistor 2I6 and the. source of potential supply 2" is connected to the anode of tube 2 through the magnetic winding 220 which is wound about a magnetic core member HI, and the latter being adapted to be energized by currents flowing through the winding 220. Positioned immediately adjacent the core member 22I is a magnetic arm member 222 which is pivoted at the point 223 and is held under restraint by a spring member 224 so that the end thereof which is remote from the core member 22I is pressed into engagement with the disc member 2I0, the latter being connected to the fiyball governor 209. The end of the arm which is normally pressed against the rotating disc 2I0 has joined thereto a friction pad 224 which bears against the surface of the disc 2I0.

The operation of the device is as follows: The two sources of potential 2" and 2I8, the resistor 2I6, the tube I and the resistance-condenser combination 2I2, 2I3 form an equivalent bridge system connected to the commutator as illustrated in Fig. 2. Thus the condenser 2I3 will have developed thereacross voltages varying in direction and amplitude according to the phase of the commutator with respect to the transmitted signal. This corrective voltage is applied directly to the grid of tube 2, the tube being biased by the resistor 2I5 so as to give a center governor setting. The plate current of the tube 2II .then controls the motor speed in either direction by varying the position of the governor control lever 222 electromagnetically by the element 22I against the force of the spring 223. The charge on the condenser 2I3 thus will vary the friction pad pressure of the governor in such a direction as to correct any speed change that might take place, and thus frame and synchronize the governor motor.

What I claim is:

1. Ai synchronizing apparatus comprising means for receiving synchronizing signals from an extrenal source, means for developing a sigsignal for controlling the rate of operation of the device to be synchronized.

2. Apparatus in accordance with claim 1 wherein said received signal and said signal developed within said apparatus are impressed on a Wheatstone bridge for comparison purposes.

3. A synchronizing apparatus comprising means for receiving synchronizing signals from a source external from said apparatus, means for rectifying said received signal, a signal generator within said apparatus, means for controlling the signal generator within said apparatus for a predeterminable .period of time by said rectified signal, means for comparing said signal from an external source and said signal generated within'said apparatus, means for storing energy in accordance with thetvalue of and of a polarity dependent upon the comparison of the compared signals, said stored energy serving as a corrective signal, and means responsive to said stored energy for controlling the speed of operation oi. the device to be synchronized.

4. Apparatus in accordance with claim 1 wherein the device to which the corrective signal is applied to control the rate of operation comprises an oscillator.

5. Apparatus in accordance with claim 3 wherein the corrective signal afiects the period of oscillation of an oscillator.

8. A synchronizing apparatus comprising means for receiving synchronizing signals from a source external to said apparatus, means for developing a signal within said apparatus at predeterminable intervals, means for comparing said received signals with said signal developed within said apparatus comprising a Wheatstone bridge, storage means electrically connected to two-non-adjacent junction points of said bridge whereby energy is storedin said storage means in .a direction and of a quantity dependent upon the comparison of said energizing signals and said signals developed within said apparatus, and means responsive to said stored energy to control the rate of operation of said device to be synchronized.

7. Apparatus in accordance with claim 6 wherein the device whose rate of operation is controlled by the stored energy comprises an oscillator. I

8. Apparatus in accordance with claim 3 wherein the device whose rate of operation is controlled by the stored energy comprises an oscillator.

9. Apparatus in accordance with claim 6 wherein the device to which the corrective signal is applied comprises a prime mover governcr.

10. Apparatus in accordance with claim 3 wherein the device to which the corrective signal is applied comprises a prime movergovernor.

11. Apparatus in accordance with claim 6 wherein the device which is controlled by said stored energy comprises a mechanical vibrating element.

12. Apparatus in accordance with claim 3 wherein the device which is controlled by said stored'energ'y comprises a mechanical vibrating element.

' MAURICE ARTZ'I'. 

